Oil pump

ABSTRACT

An oil pump includes: an inner rotor including external teeth; an outer rotor including internal teeth; a housing configured to accommodate the inner and outer rotors; an inlet port formed in the housing and configured to guide oil into a pump chamber between the external and internal teeth; an outlet port formed in the housing and configured to guide the oil to the outside of the pump chamber; and a discharge hole formed in the housing and configured to guide bubbles in the oil to the outside of the pump chamber. The discharge hole communicates with the pump chamber earlier than a timing when the pump chamber and the outlet port communicate with each other. The outlet port communicates with the pump chamber later than a timing when the pump chamber has a maximum volume.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 U.S.C. § 119to Japanese Patent Application 2017-235279, filed on Dec. 7, 2017, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to an oil pump, and in particular, to an oilpump having an inner rotor and an outer rotor.

BACKGROUND DISCUSSION

In the related art, an oil pump equipped with an inner rotor and anouter rotor has been known (see, e.g., JP 2008-308991A (Reference 1)).

Reference 1 discloses an oil pump equipped with an inner rotor havingexternal teeth, an outer rotor having internal teeth that engage withthe external teeth of the inner rotor, and a housing that accommodatesthe inner rotor and the outer rotor. The housing of the oil pump ofReference 1 is formed with an inlet port that guides oil into a pumpchamber between the external teeth and the internal teeth, an outletport which guides the oil to the outside of the pump chamber, and adischarge hole that guides bubbles contained in the oil to the outsideof the pump chamber. In the oil pump of Reference 1, the discharge holeis configured to communicate with the pump chamber in a state where thepump chamber and the outlet port communicate with each other.

In the oil pump of Reference 1, the discharge hole, which guides thebubbles contained in the oil to the outside of the pump chamber, isconfigured to communicate with the pump chamber in a state where thepump chamber and the outlet port communicate with each other. For thisreason, when the pump chamber and the outlet port communicate with eachother, the bubbles separated from the oil are disturbed by the flow ofthe outflow oil, and as a result, the effect of removing the bubblesfrom the discharge hole deteriorates. Therefore, there is a need for anoil pump capable of effectively removing bubbles contained in oil.

Thus, a need exists for an oil pump which is not susceptible to thedrawback mentioned above.

SUMMARY

An oil pump according to an aspect of this disclosure includes: an innerrotor including external teeth; an outer rotor including internal teeththat engage with the external teeth of the inner rotor; a housingconfigured to accommodate the inner rotor and the outer rotor; an inletport formed in the housing and configured to guide oil into a pumpchamber between the external teeth and the internal teeth; an outletport formed in the housing and configured to guide the oil to theoutside of the pump chamber; and a discharge hole formed in the housingand configured to guide bubbles contained in the oil to the outside ofthe pump chamber, in which the discharge hole is provided to communicatewith the pump chamber earlier than a timing when the pump chamber andthe outlet port communicate with each other, and the outlet port isprovided to communicate with the pump chamber later than a timing whenthe pump chamber has a maximum volume.

In the oil pump according to the aspect of this disclosure, the pumpchamber and the discharge hole communicate with each other before thepump chamber and the outlet port communicate with each other asdescribed above, so that bubbles may be discharged from the dischargehole, and as a result, it is possible to inhibit the bubbles separatedfrom the oil from being disturbed by a flow of the oil from the pumpchamber toward the outlet port. In addition, since the pump chamber andthe outlet port communicate with each other after the timing when thepump chamber has the maximum volume, the pressure in the pump chambermay be increased while the volume of the pump chamber is decreased fromthe state where the pump chamber has the maximum volume. Therefore, thebubbles may be discharged from the discharge hole by the increasedpressure. Therefore, the bubbles may be more efficiently discharged fromthe discharge hole, it is possible to effectively remove the bubblescontained in the oil. Here, there are water, NO_(x) (nitrogen oxide), HC(hydrocarbon), and the like as substances that degrade an engine. It hasbeen known that if water, NO_(x), and HC are contained in the oil, theoil is degraded due to chemical reactions between water, NO_(x), and HC.In the oil pump of this disclosure, it is possible to effectively removewater, NO_(x), and HC contained as bubbles in oil, and as a result, itis possible to effectively inhibit degradation of oil.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and additional features and characteristics of thisdisclosure will become more apparent from the following detaileddescription considered with the reference to the accompanying drawings,wherein:

FIG. 1 is a view illustrating an oil pump according to a firstembodiment;

FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1;

FIG. 3A is a view illustrating a state where an opening of an inlet portis closed with respect to a pump chamber;

FIG. 3B is a view illustrating a state where the pump chamber has amaximum volume;

FIG. 3C is a view illustrating a state where the pump chamber and adischarge hole communicate with each other;

FIG. 3D is a view illustrating a state where the pump chamber and anopening of an outlet port begin to communicate with each other;

FIG. 4 is a view illustrating a simulation result of pressure in thepump chamber of the oil pump according to the first embodiment;

FIG. 5 is an enlarged view of a portion from −20 degrees to 20 degreesin FIG. 4;

FIG. 6 is a view illustrating an oil pump according to a secondembodiment;

FIG. 7 is a cross-sectional view taken along line VII-VII in FIG. 6;

FIG. 8A is a view illustrating a state where bubbles are collected at anend of a groove portion; and

FIG. 8B is a view illustrating a state where bubbles are introduced intothe groove portion.

DETAILED DESCRIPTION

Hereinafter, embodiments will be described with reference to thedrawings.

First Embodiment

A configuration of an oil pump 100 according to a first embodiment willbe described with reference to FIGS. 1 to 5.

The oil pump 100 according to the first embodiment is mounted in anautomobile (not illustrated) having an engine. The oil pump 100 servesto pump oil (lubricant) in an oil pan and supply (pump) the oil to theperiphery of a piston of the engine and to moving parts (sliding parts)such as a crank shaft.

(Configuration of Oil Pump)

As illustrated in FIG. 1, the oil pump 100 has a housing 10, an innerrotor 11, and an outer rotor 12. The inner rotor 11 has external teeth111. The outer rotor 12 has internal teeth 121 that engage with theexternal teeth 111 of the inner rotor 11. Pump chambers 13 are formedbetween the external teeth 111 of the inner rotor 11 and the internalteeth 121 of the outer rotor 12.

The housing 10 accommodates the inner rotor 11 and the outer rotor 12 sothat the inner rotor 11 and the outer rotor 12 are rotatable. Thehousing 10 has an inlet port 14 that guides oil into the pump chamber 13between the external teeth 111 and the internal teeth 121. In addition,the housing 10 has an outlet port 15 that guides the oil to the outsideof the pump chamber 13. As illustrated in FIG. 2, the housing 10includes a first portion 10 a and a second portion 10 b. The inner rotor11 and the outer rotor 12 are accommodated between the first portion 10a and the second portion 10 b. The housing 10 is made of an aluminumalloy.

The inner rotor 11 is configured to be rotated by a rotating shaft 112.The rotating shaft 112 is rotated by an operation of the engine. Arotation center of the inner rotor 11 is eccentric only by apredetermined degree with respect to a rotation center of the outerrotor 12. When the inner rotor 11 is rotated in a direction of the arrowR (clockwise), the outer rotor 12 is rotated in the same direction.During the rotation, the external teeth 111 of the inner rotor 11 andthe internal teeth 121 of the outer rotor 12 mesh with each other at aportion where a distance between the inner rotor 11 and the outer rotor12 is short. In contrast, because the number of external teeth 111 ofthe inner rotor 11 is smaller by one than the number of internal teeth121, a gap (pump chamber 13) is formed between the external teeth 111and the internal teeth 121 at a portion where the distance is long. Inaddition, the pump chamber 13 is expanded or contracted simultaneouslywith the rotation in the direction of the arrow R, so that a pumpingfunction is created. Therefore, as a volume of the pump chamber 13 isincreased, the oil is sucked into the pump chamber 13. In addition, asthe volume of the pump chamber 13 is decreased, the oil in the pumpchamber 13 is ejected to the outside.

The inlet port 14 has an opening 141 at a portion where the pump chamber13 is gradually expanded. The inlet port 14 is connected to the oil pan,so that the oil is supplied from the oil pan. The outlet port 15 has anopening 151 at a portion where the pump chamber 13 is graduallycontracted. The outlet port 15 is connected to oil supply destinationsof respective parts in the engine. As illustrated in FIG. 2, the inletport 14 and the outlet port 15 are formed in a concave shape in an innersurface of the housing 10 (a surface opposite to a side at which theinner rotor 11 and the outer rotor 12 are rotatably fitted). Inaddition, the inlet port 14 and the outlet port 15 are formed in thehousing 10 so as to have predetermined flow path shapes.

In the first embodiment, the housing 10 has a discharge hole 16 thatguides bubbles contained in the oil to the outside of the pump chamber13. As illustrated in FIG. 2, the discharge hole 16 communicates withthe outside of the housing 10. Specifically, an opening 161 of thedischarge hole 16 communicates with the gap between the rotating shaft112 and the housing 10. Therefore, the bubbles discharged from thedischarge hole 16 are discharged to the outside of the housing 10.

As illustrated in FIG. 1, the discharge hole 16 is formed to be openedat a position which is closer in a radial direction to the rotatingshaft 112 than the opening 151 of the outlet port 15. In addition, thedischarge hole 16 is formed to be opened at the portion which is closerin the radial direction to the rotating shaft 112 than the opening 141of the inlet port 14. The opening 161 of the discharge hole 16 is formedto be connected to the pump chambers 13 in the vicinity of tooth bottomsof the external teeth 111 of the inner rotor 11.

In the first embodiment, the inlet port 14 is provided to be closedearlier than the timing when the pump chamber 13 has a maximum volume.Specifically, the inlet port 14 is provided to be closed earlier thanthe timing when the pump chamber 13 has the maximum volume so thatpressure in the pump chamber 13 becomes pressure that generates bubbles.For example, in a state where the pump chamber 13 has the maximumvolume, the pressure in the pump chamber 13 is configured to be lowerthan vapor pressure of water at a room temperature (about 25° C.). Inaddition, the outlet port 15 is provided to communicate with the pumpchamber 13 later than the timing when the pump chamber 13 has themaximum volume.

In the first embodiment, the discharge hole 16 is provided tocommunicate with the pump chamber 13 earlier than the timing when thepump chamber 13 and the outlet port 15 communicate with each other.Specifically, the discharge hole 16 is formed to be opened at aposition, between the opening 141 of the inlet port 14 and the opening151 of the outlet port 15, which is closer to the opening 151 of theoutlet port 15 than the opening 141 of the inlet port 14. In addition,the discharge port 16 is provided to communicate with the pump chamber13 later than the timing when the pump chamber 13 has the maximumvolume. A region where the outlet port 15 and the pump chamber 13communicate with each other and a region where the discharge hole 16 andthe pump chamber 13 communicate with each other partially overlap witheach other. That is, the pump chamber 13 communicates with the dischargehole 16 first. Thereafter, the pump chamber 13 communicates with theoutlet port 15 in the state where the pump chamber 13 communicates withthe discharge hole 16. Further, the pump chamber 13 communicates withthe outlet port 15 even after the communication between the pump chamber13 and the discharge hole 16 is closed.

As illustrated in FIG. 3A, the communication between the inlet port 14and the pump chamber 13 is closed earlier than the timing when the pumpchamber 13 (hatched area) has the maximum volume. That is, the opening141 of the inlet port 14 is formed to be terminated at a positionopposite in a rotation direction to the position at which the pumpchamber 13 has the maximum volume. When the pump chamber 13 (hatchedarea) is rotated in the direction of the arrow R from the state in FIG.3A, the pump chamber 13 has the maximum volume in the state in FIG. 3B.In this case, the pump chamber 13 does not communicate with any one ofthe inlet port 14, the outlet port 15, and the discharge hole 16.

When the pump chamber 13 is rotated in the direction of the arrow R fromthe state in FIG. 3B, the pump chamber 13 communicates with thedischarge hole 16 in the state in FIG. 3C. In this case, the pumpchamber 13 does not communicate with the inlet port 14 and the outletport 15. That is, in the state in FIG. 3C, the pump chamber 13communicates with the discharge hole 16, so that the bubbles aredischarged from the discharge hole 16.

When the pump chamber 13 is rotated in the direction of the arrow R fromthe state in FIG. 3C, the pump chamber 13 communicates with the outletport 15 in the state in FIG. 3D. In this case, the pump chamber 13 doesnot communicate with the inlet port 14. In addition, the pump chamber 13communicates with the discharge hole 16. Thereafter, when the pumpchamber 13 is rotated in the direction of the arrow R, the communicationbetween the pump chamber 13 and the discharge hole 16 is terminated.

(Explanation of Pressure in Pump Chamber of Oil Pump)

FIGS. 4 and 5 illustrate a relationship between a rotation angle(degree) of the inner rotor 11 and pressure (kPa) in the pump chamber 13in the oil pump 100 of the first embodiment. A position at which therotation angle of the inner rotor 11 is 0 degree is a closing timingposition in the related art. In addition, the pressure in the pumpchamber 13 is pressure relative to atmosphere. As illustrated in FIG. 4,the pressure in the pump chamber 13 is increased in a range in which therotation angle of the inner rotor 11 varies from about 20 degrees to 40degrees. In this case, the pressure in the pump chamber 13 is increasedup to a maximum of 12 Mpa. That is, it is possible to eject the oil withhigh pressure by retarding the opening timing of the outlet port 15. Inaddition, since the pressure in the pump chamber 13 is increased, thedischarge hole 16 is provided in this region to make it possible toefficiently discharge the bubbles.

As illustrated in FIG. 5, when the suction timing is closed 10 degreesearlier, the pressure in the pump chamber 13 is decreased, so thatabsolute pressure in the pump chamber 13 becomes equal to or lower than3 kPa which is lower than the atmospheric pressure. 3 kPa is pressure atwhich water boils at 25° C. Therefore, in the pump chamber 13, water,which is an impurity, is educed as gas.

Effect of First Embodiment

The following effects may be obtained in the first embodiment.

In the oil pump 100 of the first embodiment, bubbles may be efficientlydischarged from the discharge hole 16, as a result, it is possible toeffectively remove bubbles contained in oil. In addition, in the oilpump 100 of the present embodiment, it is possible to effectively removewater, NO_(x) (nitrogen oxide), and HC (hydrocarbon) contained in oil asbubbles, and as a result, it is possible to effectively inhibitdegradation of oil.

In the first embodiment, the bubbles may be discharged from thedischarge hole 16 immediately before the oil is ejected from the opening151 of the outlet port 15 after the oil is sucked into the pump chamber13 from the inlet port 14. Therefore, it is possible to efficientlydischarge the bubbles from the discharge hole 16 without causingturbulence of the oil in the pump chamber 13.

In the first embodiment, the pump chamber 13 is further expanded afterthe oil is sucked into the pump chamber 13 from the inlet port 14, andas a result, it is possible to decrease the pressure in the pump chamber13. Therefore, unnecessary substances such as water dissolved, as aliquid, in the oil may be educed (vaporized) as bubbles, and as aresult, it is possible to easily discharge unnecessary substances suchas water as bubbles from the discharge hole 16.

In the first embodiment, unnecessary substances dissolved in the oil maybe assuredly educed (vaporized) as bubbles, and as a result, it ispossible to effectively remove unnecessary substances from the oil.

In the first embodiment, the bubbles, which are moved toward the insideof the pump chamber 13 due to an influence of centrifugal force becausethe bubbles have a smaller specific weight than the oil, may be easilydischarged from the discharge hole 16 opened at the inside of the pumpchamber 13.

Second Embodiment

Next, a second embodiment will be described with reference to FIG. 6 toFIGS. 8A and 8B. In the second embodiment, a configuration in whichgroove portions 113 are formed in the inner rotor 11 unlike the firstembodiment will be described as an example. In addition, in thedrawings, constituent elements identical to the constituent elements inthe first embodiment are denoted by the same reference numerals as theconstituent elements in the first embodiment.

An oil pump 200 according to the second embodiment is mounted in anautomobile (not illustrated) having an engine. The oil pump 200 servesto pump oil (lubricant) in an oil pan and supply (pump) the oil to theperiphery of a piston of the engine and to moving parts (sliding parts)such as a crank shaft.

(Configuration of Oil Pump)

As illustrated in FIG. 6, the oil pump 200 has a housing 10, an innerrotor 11, and an outer rotor 12. The inner rotor 11 has external teeth111. The outer rotor 12 has internal teeth 121 that engage with theexternal teeth 111 of the inner rotor 11. Pump chambers 13 are formedbetween the external teeth 111 of the inner rotor 11 and the internalteeth 121 of the outer rotor 12.

The housing 10 accommodates the inner rotor 11 and the outer rotor 12 sothat the inner rotor 11 and the outer rotor 12 are rotatable. Thehousing 10 has an inlet port 14 that guides oil into the pump chamber 13between the external teeth 111 and the internal teeth 121. In addition,the housing 10 has an outlet port 15 that guides the oil to the outsideof the pump chamber 13.

The inner rotor 11 is configured to be rotated by a rotating shaft 112.The inner rotor 11 is rotated in a direction of the arrow R (clockwise).The outer rotor 12, which engages with the inner rotor 11, is rotatedtogether with the inner rotor 11.

In the second embodiment, the inner rotor 11 has the groove portions 113formed in tooth bottom portions 111 a of the external teeth 111. Inaddition, the groove portions 113 are formed in the tooth bottomportions 111 a of the multiple external teeth 111, respectively. Asillustrated in FIG. 7, the groove portions 113 are provided in both endsurfaces of the inner rotor 11 in the direction of the rotating shaft.In addition, the groove portion 113 is formed to have a largercross-sectional area than a bubble. For example, the groove portion 113has a depth and a width of several millimeters.

In the second embodiment, as illustrated in FIG. 6, the housing 10 has adischarge hole 16 that guides bubbles contained in the oil to theoutside of the pump chamber 13. The discharge hole 16 communicates withthe outside of the housing 10. Specifically, an opening 161 of thedischarge hole 16 communicates with a gap between the rotating shaft 112and the housing 10. Therefore, the bubbles discharged from the dischargehole 16 are discharged to the outside of the housing 10.

In the second embodiment, the outlet port 15 is provided to communicatewith the pump chamber 13 later than the timing when the pump chamber 13has a maximum volume. In addition, the discharge hole 16 is provided tocommunicate with the pump chamber 13 earlier than the timing when thepump chamber 13 and the outlet port 15 communicate with each other. Inaddition, the discharge hole 16 is formed to be opened at a position, ina radial direction, which overlaps with the groove portion 113 but doesnot overlap with the pump chamber 13. That is, the pump chamber 13 andthe discharge hole 16 are configured to communicate with each otherthrough the groove portion 113.

The groove portion 113 of the inner rotor 11 is formed in an arc shapewhen viewed in the rotating shaft. In addition, the groove portion 113of the inner rotor 11 is formed such that both ends of the grooveportion 113 are connected to the pump chamber 13. As illustrated inFIGS. 8A and 8B, as the inner rotor 11 rotates, the oil is moved bycentrifugal force from the arc-shaped groove portion 113 into the pumpchamber 13. In this case, the oil flows out from one end of the grooveportion 113, so that attractive force is generated at the other end.Further, bubbles 20, which are moved to the tooth bottom portion 111 aof the inner rotor 11, are drawn into the groove portion 113. That is,the bubbles 20 are introduced into the arc-shaped groove portion 113 bya pump-priming effect. The groove portion 113 and the discharge hole 16communicate with each other in a state where the bubbles 20 arecollected in the groove portion 113, so that the bubbles are dischargedfrom the discharge hole 16.

The other configurations of the second embodiment are identical to thoseof the first embodiment.

Effect of Second Embodiment

The following effects may be obtained in the second embodiment.

Similar to the first embodiment, in the second embodiment, it ispossible to effectively remove the bubbles contained in the oil.

In the second embodiment, the bubbles 20, which are moved toward theinside of the pump chamber 13 due to an influence of centrifugal forcebecause the bubbles have a smaller specific weight than the oil, may becollected in the groove portion 113 provided in the tooth bottom portion111 a of the inner rotor 11. Therefore, the groove portion 113 and thedischarge hole 16 communicate with each other, so that the bubbles maybe easily discharged.

In the second embodiment, the bubbles 20 may be smoothly guided into thegroove portion 113, so that the bubbles 20 may be effectively collectedin the groove portion 113.

In the second embodiment, the oil in the groove portion 113 isdischarged into the pump chamber 13 from one end of the groove portion113, so that the bubbles may be guided to be sucked into the grooveportion 113 from the other end of the groove portion 113, and as aresult, it is possible to more effectively collect the bubbles in thegroove portion 113.

In the second embodiment, the discharge hole 16 and the pump chamber 13are not directly connected to each other, and as a result, it ispossible to inhibit the oil in the pump chamber 13 from being dischargedfrom the discharge hole 16.

The other effects of the second embodiment are identical to those of thefirst embodiment.

Modified Example

Further, it should be considered that all of the disclosed embodimentsare illustrative in all aspects but not limitative. The scope of theembodiments disclosed here are defined by the appended claims instead ofthe description of the embodiments and includes all alterations(modified examples) within the meanings and scope equivalent to theclaims.

For example, in the first and second embodiments, an example in whichthe embodiment disclosed here is applied to the oil pump for supplyingoil (lubricant) to the engine (internal combustion engine) has beendescribed, but the embodiment disclosed here is not limited thereto. Forexample, the embodiment disclosed here may be applied to an oil pump forsupplying an AT fluid (AT oil) to an automatic transmission (AT) thatautomatically switches a gear ratio in accordance with a rotationalspeed of an internal combustion engine. In addition, the embodimentdisclosed here may be applied to an oil pump for supplying a lubricantto a sliding portion in a continuously variable transmission (CVT)capable of changing a gear ratio continuously without a stage unlike theAT (multistage transmission) that performs the gear shift operation bychanging a combination of gears. In addition, the embodiment disclosedhere may be applied to an oil pump for supplying power steering oil to apower steering device that performs steering (operates a steeringdevice) in a vehicle.

In the first and second embodiments, the configuration in which the oilpump is rotationally operated by the operation of the engine has beendescribed as an example, but the embodiment disclosed here is notlimited thereto. In the embodiment disclosed here, the oil pump may berotationally operated by an electric motor.

In the first and second embodiments, the configuration in which theouter rotor is driven by driving the inner rotor has been described asan example, but the embodiment disclosed here is not limited thereto. Inthe embodiment disclosed here, the inner rotor may be driven by drivingthe outer rotor.

In the first and second embodiments, the configuration in which the pumpchamber and the outlet port communicate with each other in the statewhere the pump chamber and the discharge hole communicate with eachother has been described as an example, but the embodiment disclosedhere is not limited thereto. In the embodiment disclosed here, the pumpchamber and the outlet port may communicate with each other after thepump chamber and the discharge hole are closed. Further, the pumpchamber and the outlet port may communicate with each other at the sametime when the pump chamber and the discharge hole is closed.

In the first and second embodiments, the configuration in which theinlet port is closed earlier than the timing when the pump chamber hasthe maximum volume has been described as an example, but the embodimentdisclosed here is not limited thereto. In the present embodiment, theinlet port may be closed at the timing when the pump chamber has themaximum volume.

In the first and second embodiments, the configuration in which thedischarge holes are provided at both sides of the housing in thedirection of the rotating shaft has been described as an example, butthe embodiment disclosed here is not limited thereto. In the presentembodiment, the discharge hole may be provided at one side of thehousing in the direction of the rotating shaft.

In the second embodiment, the configuration in which the groove portionsare provided at both sides of the inner rotor in the direction of therotating shaft has been described as an example, but the embodimentdisclosed here is not limited thereto. In the present embodiment, thegroove portion may be provided at one side of the inner rotor in thedirection of the rotating shaft.

In the first and second embodiments, the example in which the oil pumpis mounted in a vehicle such as an automobile having an engine has beendescribed, but the embodiment disclosed here is not limited thereto. Forexample, the present embodiment may be applied to an oil pump mounted infacility equipment other than the vehicle having the internal combustionengine. In addition, a gasoline engine, a diesel engine, a gas engine,and the like may be applied as the internal combustion engine.

An oil pump according to an aspect of this disclosure includes: an innerrotor including external teeth; an outer rotor including internal teeththat engage with the external teeth of the inner rotor; a housingconfigured to accommodate the inner rotor and the outer rotor; an inletport formed in the housing and configured to guide oil into a pumpchamber between the external teeth and the internal teeth; an outletport formed in the housing and configured to guide the oil to theoutside of the pump chamber; and a discharge hole formed in the housingand configured to guide bubbles contained in the oil to the outside ofthe pump chamber, in which the discharge hole is provided to communicatewith the pump chamber earlier than a timing when the pump chamber andthe outlet port communicate with each other, and the outlet port isprovided to communicate with the pump chamber later than a timing whenthe pump chamber has a maximum volume.

In the oil pump according to the aspect of this disclosure, the pumpchamber and the discharge hole communicate with each other before thepump chamber and the outlet port communicate with each other asdescribed above, so that bubbles may be discharged from the dischargehole, and as a result, it is possible to inhibit the bubbles separatedfrom the oil from being disturbed by a flow of the oil from the pumpchamber toward the outlet port. In addition, since the pump chamber andthe outlet port communicate with each other after the timing when thepump chamber has the maximum volume, the pressure in the pump chambermay be increased while the volume of the pump chamber is decreased fromthe state where the pump chamber has the maximum volume. Therefore, thebubbles may be discharged from the discharge hole by the increasedpressure. Therefore, the bubbles may be more efficiently discharged fromthe discharge hole, it is possible to effectively remove the bubblescontained in the oil. Here, there are water, NO_(x) (nitrogen oxide), HC(hydrocarbon), and the like as substances that degrade an engine. It hasbeen known that if water, NO_(x), and HC are contained in the oil, theoil is degraded due to chemical reactions between water, NO_(x), and HC.In the oil pump of this disclosure, it is possible to effectively removewater, NO_(x), and HC contained as bubbles in oil, and as a result, itis possible to effectively inhibit degradation of oil.

In the oil pump according to the aspect of this disclosure, it ispreferable that the discharge hole is formed to be opened at a position,between an opening of the inlet port and an opening of the outlet port,and closer to the opening of the outlet port than the opening of theinlet port.

With this configuration, the bubbles may be discharged from thedischarge hole immediately before the oil is ejected from the opening ofthe outlet port after the oil is drawn into the pump chamber from theinlet port, and as a result, it is possible to efficiently discharge thebubbles from the discharge hole without causing turbulence of the oil inthe pump chamber.

In the oil pump according to the aspect of this disclosure, it ispreferable that the inlet port is provided to be closed earlier than thetiming when the pump chamber has the maximum volume.

With this configuration, the pump chamber is further expanded after theoil is sucked into the pump chamber from the inlet port, and as aresult, it is possible to decrease the pressure in the pump chamber.Therefore, unnecessary substances dissolved, as a liquid, in the oil maybe educed (vaporized) as bubbles, and as a result, it is possible toeasily discharge the unnecessary substances as bubbles from thedischarge hole.

In the oil pump according to the aspect of this disclosure, it ispreferable that the discharge hole is formed to be opened at a positioncloser to a rotating shaft of the inner rotor than the opening of theoutlet port in a radial direction of the inner rotor.

With this configuration, the bubbles, which are moved toward the insideof the pump chamber due to an influence of centrifugal force because thebubbles have a smaller specific weight than the oil, may be easilydischarged from the discharge hole opened at the inside of the pumpchamber.

In the oil pump according to the aspect of this disclosure, it ispreferable that the inner rotor has groove portions provided in toothbottom portions of the external teeth.

With this configuration, the bubbles, which are moved toward the insideof the pump chamber due to an influence of centrifugal force because thebubbles have a smaller specific weight than the oil, may be collected inthe groove portion provided in the tooth bottom portion of the innerrotor, and as a result, it is possible to easily discharge the bubblesas the groove portion and the discharge hole communicate with eachother.

In this disclosure, the following configurations may be conceivedregarding the oil pump according to one aspect.

That is, in the configuration in which the groove portions are providedin the inner rotor, a groove portion of the inner rotor may be formed inan arc shape when viewed in a direction of the rotating shaft of theinner rotor.

With this configuration, the bubbles may be smoothly guided into thegroove portion, and as a result, it is possible to effectively collectthe bubbles in the groove portion.

In the configuration in which the groove portions are provided in theinner rotor, the groove portion of the inner rotor may be formed suchthat both ends of the groove portion in a rotation direction of theinner rotor are connected to the pump chamber.

With this configuration, the oil in the groove portion is dischargedinto the pump chamber from one end of the groove portion, so that thebubbles may be guided to be sucked into the groove portion from theother end of the groove portion, and as a result, it is possible to moreeffectively collect the bubbles in the groove portion.

In the configuration in which the groove portions are provided in theinner rotor, the discharge hole may be opened at a position, in a radialdirection of the inner rotor, which overlaps with the groove portion butdoes not overlap with the pump chamber.

With this configuration, the discharge hole and the pump chamber are notdirectly connected to each other, and as a result, it is possible toinhibit the oil in the pump chamber from being discharged from thedischarge hole.

In the configuration in which the inlet port is provided to be closedearlier the timing when the pump chamber has the maximum volume, theinlet port is provided to be closed earlier than the timing when thepump chamber has the maximum volume so that the pressure in the pumpchamber becomes a pressure that generates bubbles.

With this configuration, unnecessary substances dissolved in the oil maybe assuredly educed (vaporized) as bubbles, and as a result, it ispossible to effectively remove the unnecessary substances from the oil.

The principles, preferred embodiment and mode of operation of thepresent invention have been described in the foregoing specification.However, the invention which is intended to be protected is not to beconstrued as limited to the particular embodiments disclosed. Further,the embodiments described herein are to be regarded as illustrativerather than restrictive. Variations and changes may be made by others,and equivalents employed, without departing from the spirit of thepresent invention. Accordingly, it is expressly intended that all suchvariations, changes and equivalents which fall within the spirit andscope of the present invention as defined in the claims, be embracedthereby.

What is claimed is:
 1. An oil pump comprising: an inner rotor includingexternal teeth; an outer rotor including internal teeth that engage withthe external teeth of the inner rotor; a housing configured toaccommodate the inner rotor and the outer rotor; an inlet port formed inthe housing and configured to guide oil into a pump chamber between theexternal teeth and the internal teeth; an outlet port formed in thehousing and configured to guide the oil to the outside of the pumpchamber; and a discharge hole formed in the housing and configured toguide bubbles contained in the oil to the outside of the pump chamber,wherein the discharge hole is provided to communicate with the pumpchamber earlier than a timing when the pump chamber and the outlet portcommunicate with each other, and the outlet port is provided tocommunicate with the pump chamber later than a timing when the pumpchamber has a maximum volume.
 2. The oil pump according to claim 1,wherein the discharge hole is formed to be opened at a position betweenan opening of the inlet port and an opening of the outlet port, andcloser to the opening of the outlet port than the opening of the inletport.
 3. The oil pump according to claim 1, wherein the inlet port isprovided to be closed earlier than the timing when the pump chamber hasthe maximum volume.
 4. The oil pump according to claim 1, wherein thedischarge hole is formed to be opened at a position closer to a rotatingshaft of the inner rotor than the opening of the outlet port in a radialdirection of the inner rotor.
 5. The oil pump according to claim 1,wherein the inner rotor has groove portions provided in tooth bottomportions of the external teeth.
 6. The oil pump according to claim 5,wherein a groove portion of the inner rotor is formed in an arc shapewhen viewed in a direction of the rotating shaft of the inner rotor. 7.The oil pump according to claim 5, wherein the groove portion of theinner rotor is formed such that both ends of the groove portion in arotation direction of the inner rotor are connected to the pump chamber.8. The oil pump according to claim 5, wherein the discharge hole isopened at a position, in a radial direction of the inner rotor, whichoverlaps with the groove portion but does not overlap with the pumpchamber.
 9. The oil pump according to claim 3, wherein the inlet port isprovided to be closed earlier than the timing when the pump chamber hasthe maximum volume so that the pressure in the pump chamber becomes apressure that generates bubbles.